Particle Fluxes in the North-East Atlantic and Southern Ocean

• Main Author: Salter, Ian
• Format: Thesis
• Language: English
• Published: 2007
• Subjects: Southern Ocean; North East Atlantic
• Online Access: https://eprints.soton.ac.uk/145313/; https://eprints.soton.ac.uk/145313/1/Salter_2007_PhD.pdf

Concerns regarding the climatic implications of the increase in atmospheric CO2 concentrations throughout the anthropocene have provided the impetus to obtain a mechanistic understanding of oceanic processes and their role in regulating atmospheric pCO2. One important mechanism is the functioning of the biological pump which partitions carbon between the atmosphere and ocean reservoirs over relevant time scales. Current uncertainties revolve around the accuracy of upper ocean particle flux measurements, and the effect of iron and ballast minerals on the strength and efficiency of the biological carbon pump. This study documents the design and deployment of a neutrally buoyant sediment trap (PELAGRA). In the north-east Atlantic organic carbon fluxes were measured using this new technology and compared to indirect estimates of export based on 234Th and nutrient budgets. The vertical fluxes of 234Th into the traps were less than those estimated from the 234Th water column budget, which is interpreted to be the result of previous export events removing 234Th from the water column and the lateral advection of gradients of total 234Th/238U disequilibria confounding the Eulerian budgeting approach adopted. Successful simultaneous deployments in July 2006 at different depths provided a direct measurement of the attenuation of flux with depth, which at 1.8 is substantially greater than the canonical value of 0.856. PELAGRA deployments in the Southern Ocean were conducted as part of the CROZEX project, which examined the role of iron supply on bloom dynamics and subsequent export. Using a mass balance approach to account for the seasonal depletion of dissolved silica acid in surface waters and Si fluxes from the euphotic zone, potential surface export(100m) of organic carbon from +Fe bloom area was estimated to be in the order of 11-15 g C m-2, which is higher than previous estimates obtained from artificial fertilisation experiments. The issue of temporal decoupling between production and export processes was addressed ...